The present invention relates to a mounting mechanism for the seats of office chairs and, in particular, to a mounting mechanism that permits the seat to tilt both forward and backward.
There is an increasingly felt need in the office furniture field for chairs that tilt not only backward, which have long been widely available, but also tilt forward. This need has arisen primarily because of the widespread use of computer and word-processing systems by both office staff and management. It has become necessary to have chairs that afford a comfortable and ergonomically correct position under conditions of normal writing at one's table or desk and under conditions of operating a computer keyboard, which is usually located at a height lower than desk-top level. Lastly, there is also a need for office chairs that provide a slightly backward tilted position of active rest.
A number of different mounting mechanisms have been proposed to achieve these variations in the seat position with respect to the horizontal plane. Many of the mechanisms have various disadvantages, such as the provision of separate pivot shafts to provide tilting of the seat both forward and backward, which makes the mechanism of large size and requires a large number of parts and, hence, increases the cost and the possibility of malfunctioning. Furthermore, the known mechanisms provide for rotation of the seat about an axis or axes located a substantial distance from the front edge of the seat bottom, which results in large vertical movements of the front edge and requires the user to change the positions of his or her legs or to change sitting posture to compensate for the change in the height of the front edge of the seat bottom.
U.S. Pat. No. 4,131,260 (Ambasz, Dec. 26, 1978) describes and shows several embodiments of chair seat mounts that provide for tilting of the chair seat both backward and forward from a neutral position. Two sets of springs bias the chair seat toward the neutral position, one set resisting backward tilting and the other forward tilting. A lock device is provided for preventing the chair seat from tilting backward.
U.S. Pat. No. 4,345,733 (Ambasz et al., Aug. 24, 1982) discloses a chair seat mount that permits a chair seat to tilt forward from a normal upright position, to which it is biased by an adjustable spring. A lock device allows the user to lock the chair seat in the forward tilted position.
The seat mounts of the aforementioned patents provide for pivoting of the chair seat about a pivot axis located very close to the column of the chair base, which means that the front edge of the seat bottom moves a relatively large distance vertically when the chair seat is tilted from the neutral position. As mentioned above, this requires the user to change his or her sitting posture when the chair seat is tilted from the neutral position.